1. Field of the Invention
The present invention relates to a control method of a PI controller, and more particularly, to a control method of a PI controller, the method comprising detecting a switching point between a P control and a PI control by analyzing a frequency feature of a driving part.
2. Description of the Related Art
Generally, a highly advanced motor control technology has been applied to an industrial robot or a machine tool to improve their performance. A control system of this motor control technology uses a PI controller (proportional/integral controller) having a combination form of a P controller (Proportional controller) and an I controller (Integral controller).
This PI controller selectively performs a P control (proportional control) or a PI control (proportional/integral control) according to characteristics of a driving part controlled thereby. In a transient state, performing the P control makes a response time short and minimizes an occurrence of a response oscillation. Also, in a steady state, performing the PI control prevents an occurrence of an excessive overshoot and improves characteristics of the steady state of the system, such as a decrease of a steady state error and an improvement of stability.
In this conventional PI controller, a switching point between the P control and the PI control, that is a separating point between the transient state and the steady state, is determined according to whether values of reference variables, such as a velocity error, a velocity order, a position error and a torque order of the system, are within reference values.
However, in a method of detecting the switching point of the conventional PI controller, a process to select the reference variables and detect the size of the reference values of the reference variables is differently applied to each system. Consequently, the reference variables and the reference values need to be respectively determined in each system.
Additionally, in the case of a same system, the reference Variables and the reference values applied to a specific operation state are not applied optimally to an other state of the same system.
Furthermore, the reference values and the reference variables are typically determined through many trial and errors, necessarily requiring a dependence on an experienced operator.